This invention relates to a pneumatic hammer tool and more particularly, it is concerned with the pneumatic drive therefor. The drive has a cylinder and a differential piston which is slidably received in the cylinder and which has a piston rod projecting outwardly of the cylinder for cooperating with a tool bit, such as a chisel-shaped member. A pressure-controlled valve arrangement alternatingly routes compressed air in the two cylinder chambers at the one and the other side of the piston for causing reciprocation thereof. The cylinder wall is provided with at least one discharge opening which, controlled by the land of the reciprocating piston, alternatingly connects the one and the other cylinder chamber with the atmosphere to depressurize and release the compressed air from the respective cylinder chamber after the compressed air has displaced the piston.
Pneumatic hammers of the above-outlined type are known; they have a high impact rate and a superior output but are disadvantageous in that they operate with substantial noise. Swiss Pat. No. 580,476 discloses a pneumatic hammer in which a significant noise suppression is achieved by providing the piston at each end with conical chamfers which cooperate with discharge slots of very substantial length (as measured in a direction generally perpendicular to the direction of reciprocation of the piston). It has been found, however, that the long discharge slots cause substantial wear because the cylinder has, at the height level of the long slots, a relatively small surface that slidingly supports the piston.